1. Field of Invention
The present invention relates to a method of hologram exposure using light coherence to expose a photoresist applied on a substrate with a micropattern to light, and in particular to such a method that enables highly accurate alignment between a mask for hologram exposure that is used for hologram exposure and the substrate.
2. Description of Related Art
In a method of hologram exposure, a mask for hologram exposure (hologram mask) is first provided by using an original mask having a desirable pattern to be formed on a substrate. The hologram mask has a pattern apparently different from the desirable pattern to be formed on the substrate. A desirable coherent pattern is formed on the substrate by applying hologram exposure on the substrate using this hologram mask.
Related art document F. Cube, 0.5 μm Enabling Lithography for Low-Temperature Polysilicon Displays, SID 2003 Digest, 350 discloses that when applying the hologram exposure, it is necessary to form an alignment mark on the hologram mask, so that the hologram mask can be accurately aligned to the substrate. Since this alignment mark needs to be set as readable by an optical system for alignment, the mark cannot be made simultaneously with a pattern for hologram exposure. Therefore, although the pattern for hologram exposure and the alignment mark are formed on the same hologram mask, they are possibly out of alignment for several micrometers. As such, no matter how accurately the hologram mask is aligned on the substrate using the alignment mark, the coherent pattern formed on the substrate will be out of alignment.